(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Text Book Of Mechanical Engineering"

Files.                                     189

the elevation, and B the plan view. The Flat Chisel, Fig. 201,
is used to true up surfaces previous to filing; and the Round-
nosed Chisel, Fig. 202, is for chipping out concave flutings;
but the last is more of a machinist's than a fitter's tool, the lathe-
man and driller both using it for c drawing ' a centre-punch mark
or countersink, which has been begun untruly, by chipping a
little to one side of the depression so as to alter the position
of the centre, -after which the drill or square-centre is again
applied.

The point of a flat chisel is ground symmetrically on each
side, and should enclose an angle about equal to that of the V
screw-thread, viz,, 55, though a slightly smaller angle may be
used in finishing. After chipping, the surface must be further
trued by filing.

Files may be classified in two ways : (i) by the contour,
both in length and in section; (2) by the kind of cut and degree
of fineness. The length must also be stated, measured along
the edge, not including the tang. The cut may be double or
single, the latter being also called ' float' cut, but as this is prin-
cipally used for saw files, it will not be considered further. Longi-
tudinally, files may be parallel or blunt, and taper or pointed;
and in cross section they may be flat, three square or triangular,
half-round, round, and square. The fineness of cut is repre-
sented by the terms rough, middle, bastard, second-cut, smooth,
and dead-smooth, the last four only being required by the Fitter.
Safe-edge files are those left uncut on one narrow edge, to serve
in filing a surface near a corner, without destroying the truth of
that at right angles to it. Files are either machine or hand cut,
of which the latter are most in favour. It will be seen there-
fore, from the previous information, that a particular file may be
described something as follows:' 12 in. hand, taper, flat, bastard,
double-cut, safe-edge file.' As the teeth only cut in one direction
the file is analogous to a planing tool.

Scrapers still further true up a surface left by the file or
machine tool. They are made from old files, by grinding off the
teeth and sharpening the edges, and have three principal shapes
as shewn in Fig. 203 : Half-round (A), useful in scraping a bear-
ing ; three-square (B), sharpened on the long edge for truing up